The need for censorship of video material is generally accepted by most societies, for the purposes of preventing the viewing of material by persons other than the target audience. Usually, such censorship takes the form of limiting access of a certain group of people, for example children, to a certain class of material, for example pornographic or violent movies. Other uses of censorship include voluntary self-censorship in cases where a recipient of a program does not wish to be exposed to certain types of program, for example scenes of great violence, advertisements which may be considered offensive, or non-program material which interrupts movies, drama or sports broadcasts.
Being the most widely accessible form of broadcasting, television is the medium with which the problem of censorship is experienced most. Traditionally, censorship of television takes the form of either preventing possibly offensive material from being broadcast in the first place, or voluntary self-censorship, that is, switching off the receiver when material which the viewer does not wish to experience is being broadcast. Another form of self-censorship, which has gained popularity since the introduction of remote controls for television sets is the phenomenon known as "zapping". Zapping involves eliminating unwanted material by muting the receiver or changing channels for the duration of the unwanted segment. While such self-censorship offers the benefit that all classes of material remain available to those who do not find them objectionable, it suffers from the inconvenience of having to anticipate the nature of broadcasts and operate the receiver appropriately. This process is tedious and error-prone, especially where the viewer wishes to suppress program material which changes rapidly in nature, for example when the viewer desires to suppress commercial messages within an otherwise unobjectionable program. Manual censorship is therefore not an entirely satisfactory solution.
It is therefore desirable to provide means whereby display of preselected classifications of program material can be automatically suppressed.
Arrangements for automatic censorship have been previously published, but suffer from a number of serious shortcomings. The main difficulty is that automatic means for discrimination of different program classifications, for example detection of television commercials, have been complex and unreliable. One technique has been to detect television commercials by the short period of black picture and silence separating them from other program material. A typical commercial-deleter of this type is described in U.S. Pat. No. 4,319,286. This system and others like it suffer from the problem that erroneous operation occurs if there is a brief period of black and silence in a broadcast at a time other than at the beginning of a commercial break, or if there is no separation between commercials and other program material. Furthermore, such systems are unable to distinguish between resumption of desired program and further commercials at the conclusion of a commercial. Resumption of viewing or recording must therefore be controlled by some form of timing device, based on assumptions regarding the length of commercial breaks. If these assumptions are not correct, the system will fail in its function.
A much improved censorship means is described in U.S. Pat. No. 4,520,404. This system relies on a human operator to classify broadcasts, based on observation at a monitoring station. A suitably coded message is distributed from the monitoring station to the viewer's home, at which point a suitably-equipped decoder controls the television receiver or video recorder in accordance with the classification data generated by the human operator at the monitoring station. Although this invention significantly improves upon the reliability of previous methods, it nevertheless suffers significant limitations. One limitation is the difficulty of accurately predicting at the monitoring station when a change of program is going to occur, making the system somewhat error prone. Another limitation is that when the system is used under the control of one party to control the viewing of another party, for example used by parents to limit viewing by children, it is necessary to provide control means by which the class of program to be censored can be selected, and it is therefore possible for the other party to use these controls to disable the censorship, thereby defeating the function of the system. Yet another limitation is that during the period that unwanted material is being censored, the receiver is simply disabled. The viewer is therefore periodically presented with a blank screen and/or silence, which may have the undesirable effect of causing alarm when program suddenly resumes, or may be mistaken for a receiver malfunction.
The prior art methods are also deficient in that they do not provide means whereby an authorized person can selectively disable viewing of certain classifications of pre-recorded video programs.